1. Field of the Invention
The present invention relates to a negative electrode for a rechargeable lithium battery and to a rechargeable lithium battery including that negative electrode. More particularly, the present invention relates to a negative electrode including a lithium vanadium composite oxide and a rechargeable lithium battery including that lithium vanadium composite oxide.
2. Description of the Related Art
The conventional rechargeable lithium battery includes a positive active material of LiCoO2, a negative active material of graphite, and an electrolyte of a non-aqueous solution. Rechargeable lithium batteries have been widely used as a power source for electronic devices such as cellular phones, digital still cameras, digital video cameras, and laptop computers, and for providing electrical power to other portable appliances.
Carbon-based materials such as artificial or natural graphite, hard carbon, and so on have been used for a negative active material for a rechargeable lithium battery. The graphite of the carbon-based material increases discharge voltages and energy density for these batteries because it has a low discharge potential of −0.2V, compared to lithium. A battery using graphite as a negative active material has a high average discharge potential of 3.6V and has excellent energy density.
Moreover, graphite is most comprehensively used among the aforementioned carbon-based materials since graphite guarantees a better life-cycle for a battery due to its outstanding reversibility during charge and discharge cycles.
Graphite active materials however, have a low density and consequently a low capacity (theoretical capacity: 2.2 g/cc) in terms of energy density per unit volume when used as a graphite as a negative active material.
Furthermore, the use of active graphite materials involves some danger such as explosion or even combustion when a battery is misused or overcharged or otherwise abused, because graphite is likely to react to an organic electrolyte at a high discharge voltage.
In order to ameliorate these problems, substantial research on an oxide negative electrode has recently been performed. For example, a negative active material of LiaMgbVOc where:(0.05≦a≦3, 0.12≦b≦2, 2≦2c−a−2b≦5)is disclosed in Japanese Patent Publication No. 2002-216753 to Yamamoto et al., entitled Lithium Secondary Battery, Negative Electrode Material for the Same and Manufacturing Method of the Same, published on 2 Aug. 2002. Japanese Patent laid-open No. 2003-68305 to Yamamoto et al., entitled Negative Material for Secondary Lithium Battery and Its Manufacturing Method, published on 7 Mar. 2003, discloses a negative active material for a rechargeable lithium battery that includes a lithium vanadium composite oxide. In Japanese Patent laid-open No. 2003-68305, the lithium vanadium composite oxide has a significantly lower discharge potential relative to lithium to provide a rechargeable lithium battery having a high energy density.
A lithium vanadium composite oxide however, undergoes irreversible crystalline structure deterioration during charge and discharge, which contributes to the decomposition of an electrolyte. As a result, the lithium vanadium composite oxide exacerbates deterioration of the life-cycle, and thus reduces the useful life-time of a rechargeable lithium battery.